1. Technical Field
Embodiments of the present invention relate to a fluid injection device which ejects pressurized fluid, and to a medical instrument including the fluid injection device.
2. Related Art
Technology has been developed that pressurizes fluid such as water and physiological saltwater and ejects the fluid toward living tissues or the like through an injection nozzle for incision or excision of the living tissues or for other purpose (JP-A-2005-152127). This technology can incise the target tissues, such as internal organs, without damaging vascular structures such as blood vessels, and can thus reduce injuries to the surrounding tissues. Accordingly, this technology is expected to decrease the burden of surgery performed on a patient.
In addition, a technology which intermittently ejects a flow of fluid in pulses for incision of living tissues by using a small quantity of injection flow has been proposed (JP-A-2008-082202). According to this technology, fluid to be ejected is supplied to a small fluid chamber, and the small fluid chamber is then pressurized by a rapid reduction of the volume of the fluid chamber such that a pulse flow of the fluid can be ejected through the injection nozzle.
In order to eject fluid from the nozzle, the area from the fluid chamber to the tip of the injection nozzle needs to be filled with a sufficient amount of the fluid supplied to an injection unit. When bubbles are contained in the supplied fluid, these bubbles are broken when the volume of the fluid chamber is reduced. In this case, appropriate injection of the fluid through pressurization of the fluid within the fluid chamber cannot be achieved.
To overcome this problem, the technology of pulse flow injection uses a variable pump (such as a piston pump) rather than a centrifugal pump (such as vane pump), which easily generates bubbles. A volume variable pump (such as piston pump) secures a sufficient flow amount for supplying fluid to the fluid chamber without generating bubbles.
The pressure of the fluid supplied by the volume variable type pump, however, easily varies. Because of the variability in the pressure, the maneuverability of the fluid injection device easily deteriorates or is decreased. When the pressure of the supplied fluid lowers, the amount of fluid supplied falls short of the necessary injection amount of the fluid to be ejected. As a result, the injection amount decreases considerably, and the incision capability, or the reaction felt by the operator at the time of fluid injection varies extremely. Therefore, in the case of the technology for pulsed injection of a fluid, a special pump which is of the volume variable type and that is equipped to reduce pressure fluctuations as much as possible and that maintains maneuverability is needed.